Clandestine
by bravevulnerability
Summary: 'He had weaseled his way into her case and eventually, needling her for information while dangling his own in front of her had led them to an agreement, an even trade that turned into so much more.' An AU spin on Castle's time working as a private investigator.


_"C'mon, we both know it was just a one time thing."_

* * *

The knock on his open door has him lifting his head, his heart leaping in his chest at the sight of her in his office doorway.

"Well, if it isn't the dame of my dreams," he muses, watching with delight as her eyes roll with halfhearted mirth. "What brings you to my side of town, doll?"

"Cool it with the role play for a second, stud. I just got here," she reprimands, shrugging out of her coat and draping it across one of the chairs near his desk, indicating she'll likely be here awhile. He powers down his laptop. "At least let me have a drink first."

Castle nods towards the assortment of tumblers circling the bottle of rich amber liquid.

"Help yourself."

"So the lonely P.I. burning the midnight oil, huh?" she questions, her lips quirking into a coy grin as she pours herself a lick of Scotch and he feels a lick of arousal heat up his insides in turn.

It isn't her first time here and he doubts it will be her last, but his entire body still comes alive with excitement every time she walks through his door with a sultry smirk and bedroom eyes. Kate Beckett has become his favorite pastime.

"I was, but I think I could spare a break now that you're here."

"Oh?" she chuckles, sipping at her Scotch, the lovely line of her throat bobbing as she swallows. "Well, I actually came here with an idea for you."

"Oh?" he echoes.

Kate sets down her glass, sauntering around his desk to ease onto the edge near his laptop, the length of her legs brushing his office chair, her body so close and tempting.

"Yeah," she hums, biting on her lip, blatantly teasing him now. "You know how much I love your office."

He nods. He's always liked his office, but after having Kate pressed up against practically every square inch of it... he's grown to love it even more.

"But after last week…"

Castle winces and stands as understanding begins to sink in. Last week they had been in the middle of one of their usual 'meetings' when one of his clients had dropped in unannounced and strode through the unlocked door while Castle's hand was down her pants.

"We could go to my place," he suggests, spanning her waist with his hands, trying not to smirk when her hips cant beneath his palms.

"You have a daughter and a mother inhabiting your place most of the time," she reminds him, using her grip on the collar of his shirt to heave herself up from the desk, pressing her body snugly against his. "I have an empty apartment."

"I like your idea better," he decides, swooping in to steal a kiss from her mouth, groaning when she nips at his bottom lip before sucking it into the heated cavern of her mouth.

"I'll text you my address, meet you there?" she husks, smearing another kiss to his lips and sidestepping him to retrieve her coat while he nods dumbly, watching the line of her body saunter out his door.

* * *

Castle takes a cab to her apartment, his knee bouncing with anticipation throughout the entire drive over. It's been awhile since he's had a relationship that's lasted this long, not that this is actually a _relationship_, according to her.

He's only known her for a full month, but he's already screwing up and falling hard for this woman, wanting more than her body, more than she's willing to give. They had met through one of his clients, a telenovela star who had been caught up in one of her cases. He had been searching for the woman's purse, she had been searching for the killer of the woman's friend and costar, and when they had crossed paths, it had been inevitable. He had weaseled his way into her case and eventually, needling her for information while dangling his own in front of her led them to an agreement, an even trade that turned into so much more.

Now she came to his office every couple of days, usually once night has fallen and his workload has hit its quota for the evening. Sometimes he's the lonely P.I. and she's a wandering dame experiencing her first time in the Big Apple, other times she's too impatient, too hungry and desperate to act through the foreplay that comes with acquiring different identities.

Role playing is always fun, but he's starting to like it best when she's just Kate.

Kate is the one who has him writing again, creating a new world of fiction that surpasses his passion for Derrick Storm with ease and sends his interest in writing Bond withering into nothing more than simmering embers. Writing about Kate and the character she's inspired, Nikki Heat, is what keeps him up all hours of the night, into the early morning, and has him stumbling into his office with tired eyes and an extra shot of espresso in his coffee.

Kate is the one he's falling tragically in love with.

"Hey lover," she greets when he shows up on her doorstep only a half hour later and he grins as her arms twine around his neck, lifting on her toes to sip from his mouth, but he has to pull back for a moment, his gaze riveted to the cling of black satin on her body.

He's seen her in lingerie, but it's always beneath the shield of professional blouses and slimming dress pants. He's never seen her in a silken robe with her hair in loose waves that appear purposely tousled, as if she had gotten ready for him.

"You're beautiful, Kate," he murmurs, slanting his lips over hers, feeling the relief spread through his system when she doesn't protest to the personal remark and instead sinks into his kiss.

It isn't always the rip of clothing and the heated rush of sex, sometimes they share dinners, compare cases, discuss their separate lives. The last usually happens afterwards, when her body is still stained in sweat and cooling against his. She'll whisper secrets into his skin, fears and confessions that he holds close to his heart, and he sometimes indulges in the same habit, murmuring words he never imagined sharing into the curtain of her hair.

There was even one instance, a mere week ago, when she had shown up to his office before he had, using the spare key he had given her (_just in case you ever want to surprise me, Detective Beckett_), and he had found her curled in his office chair with red rimmed eyes and tears staining her cheeks. The sight of her, a woman so strong and powerful, looking so torn and broken had terrified him, but she hadn't allowed the inquiry of concern to leave his lips before she had risen from the chair, coming straight for him, begging around desperate kisses for him to just help her forget, just for a little while.

He's never able to deny her much.

Though, in return for his willing compliance, she had explained the reason for her tears afterwards, whispering the cause for the stone walls erected around her heart into the bare skin of his shoulder. She had told him about her mother's murder, about how it had shredded her to pieces that she was still trying to put back together.

"Tell me what to do," he had breathed into her hair, desperate to help, to mend her battered heart. "Kate, tell me how-"

"You help me," she had confessed, whispering her lips along the line of his jaw, sincerity in her hushed words. "Just - you already help."

He thinks that was the exact moment he knew.

He could love her.

But tonight, after not seeing her for four days due to her case load, after his troubling thoughts in the cab, he doesn't want to think about Nikki, about the status of his relationship with his muse, he just wants her.

Castle walks her backwards without breaking the meeting of their mouths and kicks the front door shut behind him, barely taking the time to examine the interior of her apartment. She sighs around his tongue when he slides a hand inside her robe, spanning his fingers over the hard ridges of her collarbones, the swell of a breast.

His fingers skirt along the rough edges of lace and he breaks their kiss to untie the robe, dropping his forehead to rest against hers as he takes in the sight of her body adorned in lace and shimmering satin. In the span of a month, he's seen her dressed in all kinds of lingerie, but he's never seen her in this piece, a navy blue teddy with a black lace trim that has his breath catching.

The robe flutters to the floor and his hands slip to the backs of her thighs, lifting her in his arms with ease. Kate cradles his face in her hands, kissing him hard as her thighs clamp around his waist and her bare heels dig into his backside.

"Mm, I've been waiting for this all week," she husks against his parted lips when she breaks away for breath and to point him in the right direction of her bedroom.

"Careful, Beckett," he murmurs, sliding one of his hands upwards to span the round curve of her ass, squeezing and reveling in the answering roll of her hips. "It almost sounds like you missed me."

He moves his lips to her jaw, traveling down the slope of her neck, sucking her flushed skin into his mouth as he goes, eliciting the low whimpering noises he's grown to love so much, burying them in his shoulder.

"Shut up," she mumbles, sinking her teeth into the fabric of his shirt that really needs to come off.

Castle chuckles, but hisses at the sharp pierce of her teeth to the juncture between his neck and his shoulder. Her favorite place to bite, to mark him as hers.

He yanks her mouth back to his with a fist in her hair, sealing his lips over hers, groaning at the scorching heat of her tongue diving deep into his mouth. They stumble through her bedroom doorway, collapsing onto the unmade bed after a few staggering steps.

He admires the sight of her splayed across the sheets before he begins undressing her, taking his time as he peels the lingerie from her skin, dodging her impatient hands when she tries to hurry him along, assisting her once she decides to devote her fingers to tugging his clothes off instead.

A whimper crawls past her lips at the naked press of his skin seconds later, her nails leaving crescent shaped marks in his back as he commits his mouth to the glistening skin of her throat, sipping at the salty pool of sweat staining her collarbones.

Kate's leg hooks at his thigh, ready to flip them over in a move he's come to recognize from their first night together in his bed, but he catches her by the calf before she can, squeezing the muscle to gain her attention.

"I want to taste you," he breathes into her mouth, tracing his fingers up and down the soft flesh of her inner thigh, watching her eyes widen and feeling her muscles tremble beneath his touch. It's not something they've ever tried together and he knows it's because it would cross a line, make things too personal, but god, if she would just let him... "Kate-"

"Yes," she gasps, teeth scraping her lower lip when he brushes a finger through the wetness between her legs, biting back his own moan at the sticky evidence of her arousal that coats his fingertips as he gently circles her clit, gentle enough to have her writhing with restless anticipation beneath him.

At her consent, he smudges one last kiss to her lips before his mouth begins its journey down the line of her quaking body. He's placed his mouth to almost every inch of her skin over the past month, but never like this, never with slow, unhurried reverence. It's always rushed in his office, so little time to explore, to worship at the altar of her body.

She rarely allows him to linger, but tonight… tonight she doesn't stop him.

"Castle," she groans, her spine arcing as he devotes his mouth to her breasts, his fingers still teasing between her legs. "Please - _fuck _\- I need-"

Her knee jerks up when he nips a path down her stomach, swirling his tongue around her navel, grazing his lips along the hollows of her hips, and he curls his free hand at her bent knee, holds her steady as he pauses between her thighs.

Her body arches again in anticipation, in offering, and his breath almost catches at the sight. She's beautiful.

And then he lowers his mouth.

Her reaction is instant, visceral, the cry that escapes her lips ringing out through the empty apartment, and he has to abandon his hold on her knee to press his palms to her abdomen, splaying his fingers over her dancing hips.

One of her legs still manages to curl over his shoulder as he attaches his mouth to her clit, her heel digging hard into his shoulder blade as he sucks on the sensitive bundle of nerves, almost painful, but so good.

Flattening his tongue over her nearly rips a scream from her throat, but he doesn't ease up, slicking his tongue through her folds, memorizing the tart but sweet flavor of her as she fills his mouth, already so close.

He hums against her, feeling her shiver at the vibrations the sound sends through her frame, and flicks her clit with his tongue, determined to make her come with his mouth alone.

"God, I can't - Rick - more," she gasps, her voice breaking apart, the set of fingers not twisted in her sheets slipping into his hair, tangling in his locks and keeping his mouth firm against her.

More is exactly what he wants. He's already hooked on her – her body, her taste, her heart. He wants more; he wants it all.

His tongue plunges inside her and her body convulses, breaking apart with his name on her lips.

He draws out her pleasure until she can't take it anymore, the fingers in his hair tugging weak but insistent, and Castle wipes his mouth on her inner thigh, feeling her muscles twitch and ripple at the action, and crawls up her body, settles at her side, watching with unhidden fascination as the final vestiges of her orgasm wrack her limbs.

Her eyes slowly flutter open and slide towards him, sleepy and sated.

"Mm, just give me a second," she hums and he can't help chuckling at the blissed out quality of her voice.

"Don't fall asleep on me, Beckett," he teases, resting his palm atop her stomach, skidding his thumb low along her abdomen.

She huffs, her eyes still closed while she finds his hand, tangling their fingers and halting his ministrations. She looks so different in the darkness of her bedroom, illuminated only by the shimmer of moonlight from the adjacent window, and god, he's turning into such a sap, but he wants this kind of view every night.

He becomes too lost in daydreams, too enraptured in possibilities so close but far out of reach, to realize the moment her eyes flash open, a smirk spreading across her lips just before she pounces, pinning him to the mattress with a mischievous grin he's come to know all too well.

"Don't worry, Castle," she murmurs, lowering her body to rest in a straddle atop his, sending frissons of electricity jolting through his veins. "I'm wide awake."

* * *

His eyes slide open to the sight of Kate Beckett sitting up on her side of the bed, sliding her arms through the dove grey button down he'd worn last night, flipping her disheveled hair over the collar.

"You have the day off, right?"

Kate's eyes find him from over her shoulder while she haphazardly slips only two buttons through their slots, her irises sparking with intrigue as they flicker from his face to his bare chest.

"Yeah," she murmurs, trapping her bottom lip between her teeth and gliding her fingers across the wrinkled sheets towards him. "Want to spend it in bed?"

How could he ever say no to that?

But wait - wait he had an idea.

"What about just the morning?" he compromises

"Sure, got somewhere to be today?" she asks in good-natured curiosity. It's one of the easier parts of their 'no strings attached' arrangement. She doesn't need to know where he is at all times, doesn't care about whom he's with or what he's doing. So she says.

Her actions sometimes contradicted her, like the night she had waltzed into his office, dressed in nothing more than a beige trench coat and red lipstick, only to find Gina sitting across from him. His ex-wife and current publisher was only there to give him another scolding, reiterating how stupid his P.I. work was in comparison to his writing, but at the sight of Kate Beckett, Gina had thankfully taken the hint.

But the flash of jealousy had become embedded in Kate's eyes from the moment she spotted the other woman and as soon as they were alone she had _mauled _him, spent half of the night locked up in his office playing the role of a jealous lover that he fails to believe required even a hint of acting.

Since then, it had become clear that regardless of their status, they were exclusive and he was all too happy about it.

"Do you have a case to wrap up?" she prods when he fails to answer and Castle quickly shakes his head, ridding himself of the last memories he may ever have of this woman if she reacts how he expects she might to his next words.

"Well, no, I was just thinking… maybe I could take you out today," he offers, swallowing hard at the quizzical look that paints her face once the words are out.

"Take me out?" she repeats, her lips quirked upwards, but utter confusion in her gaze.

"Like, you know, on a date?" Confusion falls way to horror. "Or we could stay in, we could-"

"Castle," she hedges, diverting her eyes to her twisting fingers. "That would be crossing the line. Our lines, remember?"

"You didn't seem to care about lines last night," he reminds her, sitting up against her headboard, squaring his jaw against the hurt he feels creeping up from his chest and onto his face. "Last night, it was anything goes."

Kate stares at him for a moment, a myriad of emotions swirling in her eyes, but then she merely shakes her head and stands from the bed.

"Why are you ruining this?"

"Kate," he calls when she stalks out of the bedroom. He growls to himself and shifts the covers from his lap, snagging his boxers from the floor before following after her.

She's positioned by one of the windows in her tasteful living room, arms tightly crossed over her chest and her body stiff as a board. His shirt drapes over her silhouette while the sunlight streams over her, highlighting the sharp angles of her cutting profile.

"I'm sorry," Castle says, but her posture doesn't loosen, the tension still strict along her spine. "I just - is this really all you feel for me? Lust?"

She pins her bottom lip between her teeth and drops her forehead to the glass of the window.

"Castle, I was never looking for a relationship. You knew that from the beginning."

"Neither was I," he shrugs, risking another few steps closer to her. "But we've been doing this for a while now. Is it really surprising that I want more?"

"No," she whispers, balling her fists beneath her elbows. "Which is why we never should have-"

"Don't," he murmurs, because he refuses to hear the rest of that sentence, to let her deem this some sort of mistake. "Even if I'm not what you want, you can't tell me you regret any of this."

"It's not _you _I don't want," Kate hisses, spinning from the window to finally face him. "It's become more than sex, you think I don't get that? But I can't handle anything more, I'm not ready."

Anger spills through his blood and his mouth opens without his consent, the words spewing free before he can stop them.

"That's bullshit. You can't hide in your mother's case forever, Kate."

The look she sends him is murderous, the fury in her eyes flaring gold and bright, and he almost takes a step back.

"You self-centered asshole," she spits, storming forward to shove at his naked chest, but he holds his grounds, remains standing through her halfhearted assault. "I regret ever telling you anything about me!"

"No, you don't," he bites back, catching her wrists when she goes to push him back again. "You told me those things because you trusted me, because you needed someone to finally be there for you, to listen. You hate it, but I'm good for you and you know it."

"_Good_ for me?" she scoffs, ripping her hands from his grasp and planting them on her hips. "All you are is a nice distraction for when I want to forget."

Her words burn like acid when they hit him, but she doesn't mean it, he refuses to believe she means it. She's just protecting herself and her vulnerable heart that he yearns to have a place inside of.

"Just like I'm a distraction for you," she adds with a defiant lift of her chin, but his brow furrows. "That's all we've ever been, Castle. Two people using each other for escape."

Her eyes flash, passion and fight rippling through her irises when he growls and comes towards her. Kate takes a step back, right into the wall next to the window, but he boxes her in, using the advantage of his size to trap her.

"You're a good liar, Kate," he mumbles, reaching for her hips, gaining confidence when she doesn't even try to bat his hands away. "But not when you're lying to me, not anymore."

She opens her mouth to protest, but he slants his lips over hers before she can, pins her body to the wall with his hips before she can say another word.

Kate grunts at the slam of her back into the wall, but doesn't stop him, her arms banding around him instead, her legs doing the same when he lifts her. He unbuttons the two buttons of his shirt to feel the hot press of her skin on his, but she doesn't allow him the opportunity to rip the shirt from her shoulders, her arms unyielding in their desire to wrap around his shoulders.

Her toes shove at his boxers and he kicks them off once they silk underwear have fallen to pool at his ankles. A moan slips past her lips onto his when he glides inside her and Castle cradles her head with one hand, catching her eyes, making her see.

"God, Castle," she gasps, tattooing his back with her nails. "I'll ruin you, I'll-"

"You already have," he mumbles, staunching the anguish spilling from her lips with the hard press of his own, distracting her with the plunge of his tongue inside her mouth and the breath stealing collision of their hips.

Kate mewls, clenching her fingers in the short strands of his hair and locking her ankles at the base of his spine, throwing herself into the needful rhythm, kissing him back as if she wants to climb inside him.

Her back slams into the wall with every pump of his hips, the wet slap of skin accompanying the sound, and he has to tear his mouth from hers to remember to breathe. Kate surprises him with the gentle cradle of her arm around his head, keeping him close and burying the building sobs escaping her throat against his shoulder when her orgasm crashes over them both, pulling him over the edge with her.

They're both trembling as he forces his eyes open past the lingering starbursts of pleasure, her head tilted back against the wall, the sun kissing her cheek, the bare slope of her shoulder, and he drops his lips to the illuminated patch of skin, tasting the sunlight.

Kate sighs and cards her unsteady fingers through his hair.

"Tell me to go," he murmurs into the cove her neck hiding there, but feeling her chest hitch. "I won't bother you anymore if you tell me to leave, Kate."

She practically deflates against him, a shuddering breath leaving her lungs, and he has to brace his legs to hold them both up as she curls her entire body around him, so close and intimate, he can feel the beat of her heart hammering against her ribcage to meet his.

He almost startles when she brushes her cheek to his and he feels the stain of moisture leaking from the corner of her eye onto his skin.

"Stay," she breathes, dusting her lips along line of his jaw. "I want you to stay."


End file.
